Argon gas tank size and weld time?

I'm looking to buy a tank. The local gas supply want to rent me a 300CF tank for 60$ a year. But I can buy a 80 CF tank on eBay for 145$. I would prefer to just buy my own tank. I guess the question is, on a rough guess, how many hours of weld time do you get out of a 40/80/300CF tank? (I know a lot depends on gas flow and purge time)
With an 80CF tank, if I weld an hour a night, will I be driving to the gas supply place every other week?

Theres a very simple equation:
CF of tank/CFH your gear is setup for=#hours said tank will last

For example, most people TIG with about 20CFH (no backpurge), so an 80cf tank will last 4 hours of actual welding.

A 300CF for $60/yr is pretty good, its $46/yr for a 120 here. Check refill costs too, its $40 for me to fill my 80, and 50 to fill a 240. Most of the charge is the hookup fee, little of it is the actual argon.

mrlegoman...I would not buy the tank online. Most of the gas places that supply Argon will not fill customers tanks that were not purchased from them. If you do find a place that will fill them you will also be responsable for the hydrostatic testing of the tanks every few years.

mrlegoman...I would not buy the tank online. Most of the gas places that supply Argon will not fill customers tanks that were not purchased from them. If you do find a place that will fill them you will also be responsable for the hydrostatic testing of the tanks every few years.

John

New tanks are certified for 10 years. Recert tanks are rated for 5 years. Its illegal for a company to refuse to fill a certified tank, no matter where it was bought, but they can mandate that you pay them to test it. Kinda stupid, but its always cheaper to buy locally, shipping kills you. A recert 80CF tank was $128 here.

The place I go to just swaps tanks. Makes it real quick, leave old one outside the door, in 5 mins you're paid for and out the door. The pickle I'm in is I got a 300cf tank filled with c25 for !free!, and the starting tank I bought (80cf) is empty, now I want to start TIGing. I'm thinking about renting one till my MIG uses the c25 up.

Shipping off ebay probably would suck up the savings, just make sure it comes with a cap that screws on. Last thing you'd want is a tank they won't fill because its broken.